Process for production of uniformly discharged particle flow

ABSTRACT

In a process for the production of a uniform flow of particles to be discharged over the width of a hopper, such as cellulose or mineral fibers or glue-coated chips or mixtures for the production of boards consisting of these materials, a feeding device is arranged above the hopper transversely to the longitudinal axis of the hopper for discharging particles into the hopper. A stationary feed arranged to the side of the hopper supplies particles to the feeding device. The feeding device includes a horizontal belt conveyor which carries the particles from the stationary feed to the hopper. The entire feeding device moves back and forth during this procedure whereby the particles are deposited into the hopper from one side thereof to the other. This prevents or substantially eliminates the particles from lumping or sticking together in the hopper which might otherwise occur if the particles were simply directly supplied to the hopper from a stationary source.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a division of application Ser. No.07/302,762, filed Jan. 26, 1989 now U.S. Pat. No. 4,948,322.

BACKGROUND OF THE INVENTION

The present invention relates to process and apparatus for theproduction of a uniform flow of particles discharged over the width of ahopper, for example, fibers consisting of cellulose-containing ormineral-containing materials or fibers, chips or mixtures of suchparticles provided with binders for the production of boards from thesematerials. A hopper is charged with these materials by a feeding devicearranged above the hopper transversely to the longitudinal axis of thehopper, and a stationary feed arranged to one side of the hoppersupplies the feeding device with particles.

In the production of boards from glue-coated chips, so-called chipboards or for the production of boards consisting of wood fibers orpaper fibers or boards consisting of mixtures of cellulose fibers andchips in which water and gypsum are added as a binder, it is necessarythat these particles be stored in hoppers before the production of suchboards. The main reason for storage in hoppers is that in the continuousproduction of webs from these particles, a uniform amount of theseparticles must always be on hand to prevent defects, such as defects inthe specific gravity or in the density, for example.

With this type of intermediate storage, it must also be kept in mindthat material stored for the same length of time must be supplied forfurther processing, in particularly, when this relates to glue-coatedchips for the production of chip boards or when this relates to theproduction of MDF (Medium Densitive Fibers), which also have alreadybeen glue-coated for the production of MDF boards. In order to achievethis goal, the so-called first-in first-out principle of storing inhoppers must be employed. If particles are to be mixed in a hopper, forexample, cellulose fibers mixed with wood chips, a first-in first-outstorage is not suitable since the particles of each type must be storedabove each other and then scraped by removal of the front wall ofmaterial with scraper rolls. A thorough mixing is obtained with themovement of the bottom belt of the hopper against the scraper rolls.

With intermediate storage in hoppers it is generally necessary to makesure that patches having a higher density, so-called pockets, do notoccur within the stored particles, and that the upper particle layerdoes not have irregularities transversely and longitudinally to thelongitudinal axis of the hopper. This prevents defects from occurring inthe composition and in the material amounts by scraping with the scraperrolls. To even out the upper layer, a so-called back stripper is used inthe upper region of the hopper which extends over the entire width ofthe hopper and of which the forward moving leg turns in a directionopposite to the forward moving leg of the bottom belt.

DE-PS 30 31 864 discloses a process and an apparatus for charging anintermediate hopper. Essentially following a feeding command emanatingfrom the hopper and a signal of the amount of material in the hopper tobe supplemented, a uniformly distributed chip supply is continuouslyprovided above the hopper corresponding to the hopper width. The chipsare then discharged into the hopper. A screw conveyor extending over theentire width of the hopper is especially suitable and after properrefilling with a chip supply, the screw conveyor releases these chipsover the entire width of the hopper via a discharge slot in a movabletrough. Such a device used with particles inclined to lump together inthe preparation for a uniform discharge has a tendency to compact theparticles together. Sticking of the particles to the transport meansalso occurs. With particle discharge over the entire width of the hopperthere is no guarantee that evenly distributed material remains presentin the hopper. The risk of pocket formation also exists.

DE-PS 952 565 relates to a device for providing uniform deliveries ofwood chip material or other bulk material resulting in uniformity with adischarge device known per se which takes material arriving in an evenflow and throws the material in the same or opposite direction asmovement of the delivery support. The device is narrow and moves backand forth over the delivery width. With such a discharge service auniform deposit in a hopper in the direction of and transversely to itslongitudinal axis cannot be obtained since the material arriving via aconveyor belt is separated by the influence of the discharge device. Insome areas, as explained with the example of wood chips, only large woodchips or heavy chips are deposited. In other areas transversely to thelongitudinal axis of the hopper only small or light particles aredeposited. In this disclosure, another feed is also described wherebyparticles to be deposited are discharged via a pivotable pipe. However,as a result of their discharge speed, the particles are also depositedseparately according to size and weight.

SUMMARY OF THE INVENTION

Based on the state of the prior art, one objective of the presentinvention is the preparation of a uniform particle discharge essentiallyfree of particles lumped together or compacted or stuck together. Also,a non-uniform lumping together of the particles inside the hopper isprevented when the upper layer of the added material is evened out.

By providing the same relative conveyor belt speed to the feed ofmaterial onto the belt in both the forwarding and reversing direction ofthe conveyor belt, a uniform distribution of particle flow is preparedfor discharge. In the deposit of the flow over the entire width of thehopper, a change and/or ridge formation is prevented so that in asubsequent evening out of the upper layer by a back stripper, lumpingtogether of the particles is prevented. The process of the presentinvention also provides the possibility of charging the hoppertransversely to the longitudinal axis in the forwarding and reversingdirection of the conveyor belt without a change in the composition ofthe prepared particles.

Also in shifting of the entire conveyor belt transversely to thelongitudinal axis of the hopper to be charged, unmixing of the prepareduniform particles does not occur. The possibility of separation, forexample, with too fast a rotating conveyor belt, is prevented as aresult of particle accumulation at a barrier before deposit in thehopper.

Based on the state of the art, the objective on which the invention isbased is also met with an apparatus for the production of a uniform flowof particles to be discharged over a hopper width, such as fibersconsisting of cellulose-containing or mineral-containing materials orfibers, chips or mixtures of these particles provided with binders forthe production of boards from these materials with a particular feedingdevice. The feeding device operates constantly during the chargingprocedure and extends above the hopper transversely to the longitudinaldirection of the hopper. A stationary feed is arranged to the side ofthe hopper for supplying the feeding device with particle material.

In particular, at least one motor may be provided for the simultaneousdrive of a cart moving back and forth and of a conveyor belt carried bythe cart which belt always rotates in one direction. In the forwardingdirection of the cart towards the hopper, particulate material on thebelt is not discharged from the discharge end of the belt into thehopper since the belt does not move relative to the cart. This is basedon a gear ratio of 1:1 between cart and conveyor belt and rotation inone direction. However, when the cart is pulled back to the startingposition, the uniform discharge of particle flow into the hopper takesplace, since in this case the conveyor belt moves twice as fast towardsthe hopper compared to the forward direction. Movement of the cart whichis opposed in direction to the conveyor belt produces the desired beltspeed. While the conveyor belt is pulled back by the cart, anuninterrupted particle flow is produced with the same amount of particleflow onto the belt and into the hopper from the discharge end thereof.As a result of the constant relative speed of the belt to the stationaryfeed, the same amount of particle flow is discharged.

The provision according to the invention of a boundary chute at thefront end of the cart counteracts the particle separation effect of aforming throw parabola. This barrier effect is maintained up to the wallarea of the other hopper wall so that feed defects are minimized, andseparation or slope defects at the side walls of the hopper areeliminated. If the gear ratio is changeable the hopper can also berefilled transversely to its longitudinal axis when the conveyer belt ispushed forward and pulled back by the cart. A uniform filling over abroad area in the longitudinal direction of the hopper is produced. As aresult, the evening out of the upper layer in the hopper by a backstripper is achieved in contrast to the state of the art, in which thehopper is refilled transversely to its longitudinal direction with theaddition of mounds extending transversely to the longitudinal directionof the hopper and whereby as a result of the back stripping procedurepocket formation increases. Instead of at least one drive motor for thecart and conveyor belt, one drive for the cart and another drive for theconveyor belt can also be selected.

A motor is arranged on a base plate and two drive pulleys are connectedto the drive shaft of the motor. The return pulley for the cart and thereturn pulley for the conveyor belt are also arranged on the base plate.Chains or timing belts may be used as the drive means between the drivepulleys on the motor shaft and the return pulleys. The drive means forthe cart has a pin-like arrangement connected to move with the drivemeans. A catch device on the cart is connected to move with the pin andin this way the cart is moved in a forward and backward direction. Thedrive means arranged between the other drive pulley and the secondreturn pulley is simultaneously used as a drive for the conveyor belt.

The axle distance between the drive pulley and the return pulley for thedrive of the cart is at most the same or smaller than the axle distancebetween the other drive pulley and the second return pulley provided forthe drive of the conveyor belt. As a result, the entire charging deviceto the hopper is very simply adjusted without the risk of unwantedparticle discharge next to the hopper. The adjustment is simplified to ashifting of the entire position transversely to the hopper when the axledistance between drive pulley and return pulley for the drive of thecart is adapted to the approximate hopper width.

The drive roll of the endless conveyor belt is held between two guidepulleys arranged in the forwarding leg of the drive means. A path ofthis type clearly prevents any additional sliding, and the twosuperimposed movements, i.e. movement of the conveyor belt in the samedirection and back and forth movement of the cart, are produced.

In the present apparatus not only can an electric motor be used as adrive for the cart but a back and forth moving connecting rod may alsobe employed. According to the invention, the movement of the cart iselectrically scanned and fed as a set value to a controller which isalso supplied with the actual value of a controlable DC motor for theconveyor belt drive. The conveyor belt drive may be controlled when aconnecting rod to the drive of the cart is employed, which remains atthe reversals function-related. This type of unsteady movement of thecart which also produces an unsteady deposit in the hopper represents adeposit defect over the width of the hopper which can be ignored and iscancelled out by the retained lack of lumping of the material.

The conveyor belt in its forwarding leg is constructed as a trough belt.As a result, conveyed material to be deposited in the hopper isprevented from falling off the conveyor belt and from unwantedaccumulations in the installation. For sticky material, caking of theparticle flow on the conveyor belt is also prevented at the same timesince the trough shape is not provided near the discharge end of theconveyor belt. The belt also has a belt cleaning arrangement at thefront end thereof. As a result, contamination of the installation causedby the returning leg of the belt is clearly prevented. All of theparticles on the belt are deposited in the hopper.

The invention includes an intermediate hopper for the intermediatestorage of particles for the production of boards from these particles.The intermediate hopper is uniformly charged with the most varyingparticles and their mixtures such as cellulose fibers, mineral fibersand chips in a glue-free and glue-coated state without encountering theexisting problems of lumping together or sticking or compacting of thematerial by the feed elements.

BRIEF DESCRIPTION OF THE DRAWING

Novel features and advantages of the present invention in addition tothose noted above will become apparent to persons of ordinary skill inthe art from a reading of the following detailed description inconjunction with the accompanying drawing wherein similar referencecharacters refer to similar parts and in which:

FIG. 1 is a schematic side elevational view of apparatus fortransversely charging a hopper with particle material, according to thepresent invention;

FIG. 1A is a partial schematic side elevational view of apparatussimilar to that shown in FIG. 1 illustrating a slight modification ofthat apparatus;

FIG. 2 is a top plan view of the charging apparatus and hopper shown inFIG. 1;

FIG. 3 is an enlarged fragmental view of the discharge end of thecharging apparatus shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 2;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 1; and

FIG. 6 is a schematic side elevational view of an alternate embodimentof apparatus for transversely charging a hopper with particle materialbut having a different drive system from that shown in FIGS. 1-5.

DETAILED DESCRIPTION OF THE INVENTION

In order to uniformly charge a hopper 1 with a particle flow 2,according to the exemplified embodiment of FIG. 1, a conveyor belt 4arranged on a cart 3 is supplied with particles 6 at a feed 5. Theparticles 6 may consist of glue-free or glue-coated cellulose or mineralfibers or of mixtures of such fibers or of chips and mixtures of chipswith fibers or fiber mixtures.

The drive of the conveyor belt 4 via a drive motor 7 always moves theupper forward leg of the conveyor belt 4 constructed as an endlessconveyor belt in the direction of the hopper 1. The return lower leg ofthe conveyor belt 4 always moves in the opposite direction away from thehopper. The cart 3 is also simultaneously driven by the drive motor 7via a continuous drive means 8. The continuous drive means 8 may beconstructed as a timing belt as shown in FIGS. 1 and 2 or chain 8A, asshown in FIG. 1A, and includes a pin 9 which moves with the belt orchain. The cart 3 has a catch device 10 arranged thereon and constructedto cooperate with pin 9 on continuous drive means 8. As the pin 9 moveswith the continuous drive 8 around drive pulley 12 and return pulley 13cart 3 moves back and forth due to the cooperating relationship betweenpin 9 and catch device 10. The back and forth distance traveled by thecart corresponds to an adjustable axle distance 11 between drive pulley12 and return pulley 13 (FIGS. 1 and 2) or sprocket pulley 13A (FIG.1A). The adjustable axle distance 11 between the drive pulley 12 andreturn pulley 13 arranged on a base plate 14 is necessary to uniformlyfill different width hoppers 1 with a particle flow 2 using the samecharging device.

Once the hopper is filled for the first time and such is made known bylimit switch 15, for example, the feeding device 16 essentiallyconsisting of cart 3, endless conveyor belt 4, feed 5, and motor 7 isstopped on the left side edge of the hopper 1. The removal of particles6 from the hopper 1 for the production of boards causes the storagecontent to decrease until the command for feeding new particles is givento the feeding device 16 via another limit switch 17. As a result, themotor 7 arranged on the base plate 14 is started and via its drive shaft18 the motor drives the drive pulley 12 and via this pulley the returnpulley 13. The motor 7 also drives another drive pulley 19 and via thispulley drives another return pulley 21 arranged on the base plate 14 bymeans of another drive means 20. As a result, the other drive means 20which may also consist of an endless chain drive or timing belt drives adrive roll 24 connected to the endless conveyor belt 4 via guide pulleys22, 23.

When particles 6 are present in the feed 5, they follow the particlesalready on the conveyor belt 4 which were not yet uniformly depositedinto the hopper 1 as feed flow 2 by the endless conveyor belt 4 in thepreceding feeding procedure. The conveyor belt is at the same gear ratioto the motor as the cart is to the motor. The belt is taken from astarting position 25 to a discharge position 26 as the cart is shiftedon tracks 27 via rollers 28.

Following the discharge position 26, the cart 3 is moved back in thedirection of the starting position 25 via the continuous drive means 8and the pin 9 and catch mechanism 10. Simultaneously a uniform feed flow2 is released over the width of the hopper 1 into the hopper by theendless conveyor belt, the speed of which now increases from zero todouble speed. At the same time, the endless conveyor belt 4 moves fromthe right to the left and as a result of its double speed at the samegear ratio between motor and cart as motor and conveyor belt drive. Thebelt is constantly provided with a particle amount 6 as released by theparticle flow 2 in the hopper 1 over its width. At the same time, duringthe feeding procedure, a back stripper device 29 in the hopper with itsforward leg 30 runs opposed to the bottom belt 32 of the hopper 1constantly turning in the direction of arrow 31 during the chargingprocedure. The particle material deposited over a partial length 33 ofthe hopper is, therefore, added by means of the back stripper device 29to the already supplied particles without the formation of pocketsbetween the already stored and the newly added particles caused byirregularity during the feeding procedure. Feed is continued until thefeeding device 16 is stopped via the limit switch 15 on the left edge ofthe hopper 1.

In other words, when cart 3 and endless conveyor belt 4 move forwardfrom starting position 25 to discharge position 26 by the action ofdrive 8, pin 9 and catch 10, the belt 4 is continuously drived by agiven amount. However, this forward drive of the belt is negated by themovement of belt roller 24 along drive 20 which drives the belt in thereverse direction by the same given amount. Hence, movement of the beltappears stationary except for the forward movement imparted to the beltby the cart moving from starting position 25 to discharge position 26.Feed 5 deposits particles onto the belt but no material is dischargedfrom the belt into the hopper due to the relative stationary nature ofthe belt during this forward movement. When the cart 3 and endlessconveyor belt 4 move away from the hopper from discharge position 26back to starting position 25, belt 4 continues to be driven a givenamount by drive 20. However, this forward drive of the belt is nowdoubled by the movement of belt roller 24 along drive 20. Substractingthe return movement of the cart produces a relative belt speed identicalto the belt speed during the forward movement. Hence, during both theforward and return movements of the belt and cart, the relative movementbetween stationary feed 5 and belt 4 remains the same, and anuninterrupted uniform flow of particles is deposited onto the belt. Thismaterial is discharged from the belt into the hopper but only during thereturn movement of the belt and cart to starting position 25.

The front discharge end of the endless conveyor belt 4 has a boundarychute 34 arranged between rolls 28 running on parallel tracks 27 andalways having the same distance to the front guide pulley 35 of theendless conveyor belt 4. A doctor blade 36 is at the same time arrangedon the front guide pulley 35 supported on the cart 3 and placed inworking relationship with the returning leg of the endless conveyor belt4. This assures that after the belt discharge at the endless conveyorbelt 4, any still adhering particle material is definitely added evenlyagain to the particle flow 2 in the same depositing procedure while aseparation of the particle flow 2 is absolutely prevented by theboundary chute 34.

The endless conveyor belt 4 is in the shape of a trough in the forwardleg of conveyor belt movement. Appropriately shaped rolls 37 give theconveyor the trough shape as shown best in FIG. 4. The return leg of theendless conveyor belt 4 is guided back via straight support rolls 38.The frame 39 of the endless conveyor belt 4 is connected with the cart3.

As shown best in FIG. 5, the particles 6 fed into the hopper 1 areremoved from the particle supply via scraper rolls 40 rotating in thedirection of the arrow. The particles are fed as a delivery flow 41, forexample, via a distributor 42 to devices (not shown) for the productionof boards from fibers or chips or their mixtures.

If the gear ratio between the other drive pulley 19 on the drive shaft18 of the drive motor 7 and the other return pulley 21 is changed insuch a way that the drive roll 24 of the conveyor belt 4 rotates athigher speed, charging the hopper occurs at a faster rate. For aconstant deposit of particles 6 on the conveyor belt 4 when the cart 3runs from the stationary position 25 of the conveyor belt 4 to thedischarge position 26 of the conveyor belt 4, a uniform particle flow isalready released into the hopper 1 so that a much shorter charging ofthe hopper 1 is obtained.

The feeding device 16 can be adapted to different width hoppers 1 whenthe axle distance 11 between the return pulley 13 and the drive pulley12 is changed. It must be kept in mind, however, that the axle distance11 at most equals the other axle distance 43 (FIG. 2) between the otherdrive pulley 19 and the other return pulley 21 so that the feedingdevice can only be adapted to the different hopper widths by changingthe belt width of the endless conveyor belt 4 and by changing the axledistance 11.

Instead of the one motor 7 with one drive shaft 18, a motor having twoshaft ends may be provided. Also, instead of one drive motor 7, twodrive motors adapted to each other in their speed may be provided toguarantee that the conveyor belt 4 always has the same relative speed tothe feed 5 when the conveyor belt is pushed forward and pulled backunder the stationary feed 5.

A rack and pinion driven by a drive motor 7 may be used for the purposeof moving the cart 3 back and forth. Also, a hydraulic drive may effectthe back and forth movement of the cart 3 in such a way that therelative speeds of the endless conveyor belt 4 and the feed 5 are thesame in both the forward and reverse directions.

In the drives and driving means, reversals employed in the embodimentaccording to FIGS. 1 to 5, in particular, in the reversal of the cart 3from the forward to the reverse movements, a constant path is producedwhich is attuned to the acceleration of the coveyor belt from theacceleration zero at the forward movement of the cart 3 when cart 3 andconveyor belt 4 have the same speed at the same gear ratio, to anacceleration corresponding to double the speed of the endless conveyorbelt 4 when the cart 3 is pulled back. If the above mentioned equallyoperating drive rack and pinion or a pneumatic drive is used, a constantzero passage or else a constant transition from the forward to thebackward movement of the cart are not obtained but this transition canonly be obtained by a standstill of the cart between the forward andreverse movements.

In the charging device shown in FIG. 6, the conveyor belt is driven by adrive motor 51 connected with a tachometer generator 52. A motor 50separately arranged constantly moves the cart 3 in the exemplifiedembodiment back and forth via the continuous drive means 8. Instead ofthe drive motor 50 and the drive means 8, a rod drive may also be usedin which a back and forth movement of the cart 3 is conducted andwhereby the cart 3 always remains at the reversal points. Via anothertachometer generator proportional to the movement of the cart and,depending on the forward pushing or reverse movement of the cart 3,produces a positive or negative voltage. This signal is impressed on aDC voltage emitted by a DC voltage source 56 so that the set value forthe movement of the cart is available at a branch point 57. This setvalue is fed to a controller 53 which is supplied with the actual valueby the tachometer generator 52. As a result, a control voltage for themotor 51 is available at the output 58 of the controller 53 by means ofwhich the speed of the drive motor 51 is controlled in such a way thatthe same discharge amount is always released into the hopper.

The speed of the endless conveyor belt is, therefore, adapted to theshifting movement of the cart 3 in such a way that the relative speedsof the conveyor belt 4 and the feed during forward and reverse movementsare the same. As mentioned above, this provides for the possibility ofusing a catch pin which runs back and forth and which may be driven by ahydraulic cylinder instead of the drive for the cart 3 by means of arotating chain and catch bolts.

The drive motor 51 of the conveyor belt may also be modified byswitching the poles or controlling the frequency. The movement of thecart 3 can then be conducted via switching elements which detect aposition of the belt cart. In this way, the speed of the conveyor belt 4can be controlled by means of a control switch in such a way that thespeed of the belt 4 relative to the feed 5 is always the same.

What is claimed is:
 1. A process for the production of a uniform flow ofparticles to be discharged over the width of a hopper, such as fibersconsisting of cellulose-containing or mineral-containing materials orfibers, chips or mixtures of such particles provided with binders forthe production of boards from these materials by charging a hopper witha feeding device arranged above the hopper transversely to thelongitudinal axis of the hopper and with a stationary feed to the sideof the hopper that supplies particles to the feeding device, the processcomprising the steps of arranging a horizontal endless belt conveyorwith a discharge end above the hopper, shifting the entire conveyor in aback and forth direction so that the discharge end traverses the hopperfrom side-to-side thereof in a forward direction toward the hopper and abackward direction away from the hopper, driving the endless belt of theconveyor in the same direction at a given speed, shifting the entireconveyor back and forth at the same or higher speed as the belt of theconveyor to render the relative belt speed zero or higher when theentire conveyor is shifted in the forward direction toward the hopperand twice as high or higher than the belt conveyor when the entireconveyor is shifted in the reverse direction away from the hopperwhereby the speed of the endless belt relative to the stationary feedremains the same when the entire conveyor is shifted back and forth, andsupplying the width of the endless belt with material from thestationary feed.
 2. A process according to claim 1 including the step ofguiding the particles into the hopper as they are dropped from thedischarge end of the endless conveyor belt.